One conventional approach to antenna assemblies for satellite communication has been to provide paraboloid shapes, i.e., a dish shape, and point it towards a satellite. This is an efficient and cost effective solution for ground based installations, especially for communication with geostationary satellites. It has also been satisfactory for some vehicle applications, such as in the maritime industry where vessels travel at relatively low speeds in which a low profile antenna assembly is not critical for drag reduction. Further, greater weight and power requirements are more easily tolerated for marine surface vessels.
Some attempts have been made to provide paraboloid types of antennas on aircraft. However, the applications have been limited to areas where the antenna can be enclosed behind a radome to reduce drag. This has constrained the size of the antenna assembly, and hence performance. In addition, aircraft move at a much greater rate of speed relative to marine vessels and difficulties are frequently encountered in maintaining proper orientation of the assembly relative to a satellite, i.e., keeping the assembly pointed towards the satellite. While satisfactory for some military and business applications, other solutions have been attempted for aircraft used for commercial passenger transport, such as planar arrays of antennas configured to cooperatively act together in a phased array.
Instead of a large paraboloid structure for concentrating and directing a signal, a planar antenna array employs a group of smaller antenna elements. In particular, the signals from each element of the array are combined to produce a beam having a predefined shape and direction. Beam direction is changed as needed via a control system that adjusts the phase and gain of signals transmitted and received to and from the elements of the array to combine individual signals to shape and direct the beam.
The advantage of planar phased arrays for use on vehicles, especially aircraft, is the low profile of the array. Namely, the arrays can be formed to have a substantially planar surface. However, there are drawbacks, of which a major one is the limited range of angles through which the beam may be directed or steered. In the past, the range has been limited to directions deflecting the beam from about 45 degrees to 60 degrees from perpendicular to the plane of the array. While steering the beam to angles beyond this range is possible, reception and transmission performance tends to degrade rapidly. Attempts have been made to expand the effective deflection range by making the planar array rotatable about one or more axes. While making the array rotatable does expand the range of angles over which nominal reception and transmission performance may be maintained, it requires the addition of mounting structure providing rotatable axes that adds significant weight. Moreover, the mounting structure requires space for the mounting structure itself and permitting rotations of the array, which increases the profile height of the resulting antenna assembly. Further, repeatedly rotating the planar array tends to reduce the mean time between failures (MTBF).
Finally, it requires power to operate the phased array, which results in significant waste heat that must be dissipated. This can be difficult because the radome enclosing the antenna assembly traps heat, and excessive temperatures degrades performance of the array. Moreover, the power required by the phased array results in increased fuel consumption. Accordingly, better solutions are desired.